In a wiring process of a semiconductor device, an interlayer dielectric film disposed between wiring layers is etched for conducting the wiring layers. In view of the recent demand for higher speed of a semiconductor device, an interlayer dielectric film has been required to have a lower dielectric constant, and an organic material film has been used as such a low dielectric constant film.
An organic material film is etched with plasma, using an inorganic material film, such as silicon oxide, as a mask. To be specific, as disclosed in Japanese Patent Laid-Open Publications No. 2001-60582 and No. 2001-118825, the plasma-etching process is carried out by means of a plasma-etching apparatus, in which a pair of parallel plate electrodes facing vertically each other are disposed in a process vessel. A semiconductor wafer (hereinafter referred to simply as “wafer”) is placed on a lower electrode (support electrode) which is one of the pair of parallel plate electrodes, and a high-frequency power of a frequency of 13.56 MHz is supplied to the support electrode. A gas including N2, H2, Ar and the like is supplied as a process gas to the process vessel.
The conventional plasma-etching process of an organic material film carried out under the above-described conditions has the following disadvantages. That is, when a plasma density is increased for a higher etching rate, a self-bias voltage of the electrode is also increased. Thus, a facet formation of an inorganic material film, which is disposed adjacent to the organic material film to serve as a mask, is damaged by drawn ions, resulting in a deterioration in etching selectivity of the organic material film relative to the inorganic material film. Namely, a high etching rate and a high etching selectivity cannot be simultaneously attained.
A possible method of etching an organic material film with a high selectivity while preventing such a facet formation damage is to use a molecular single gas or mixed gas, excluding an atomic gas such as Ar gas having a high etching action (high sputtering action). This method is, however, disadvantageous in terms of a considerably degraded uniformity in electron density (plasma density), in accordance with an electric field strength distribution. That is, a center portion of the substrate has a higher electron density, while an edge portion thereof has a lower electron density. Therefore, a resulting etching uniformity is unavoidably lowered. In particular, when a wafer has a large diameter of, e.g., 300 mm, such non-uniformity in the electron density (plasma density) is noticeably deteriorated.